Method of cleaning and pickling metals



Patented Nov. 3, 1931 UNITED STATES Examines PATENT OFFICE WALDO L.SEMON, OF CUYAHOGA FALLS, OHIO, ASSIGNOR TO THE B. F. GOOIDRICH COM- rm,NEW YORK, N. Y, A CORPORATION OF NEW YORK METHOD OI CLEANING No Drawing.Application filed December This invention relates to the art of picklingmetals such as iron or steel, that is, to the art of removing scale orrust from the surface of such metals by a process of solution.

It is the common practice to remove scale and rust from the surface ofiron or steel by immersion in a dilute solution of sulphuric or muriaticacid, which is frequently heated to a temperature of about 70 C. toaccelerate the solution of the iron oxides.

However, the pickling acid, in addition to its dissolving action on theoxides, rapidly attacks the metal itself, dissolving it and liberatinghydrogen gas. The hydrogen gas escaping from the liquid carries with itsome of the acid in the form of a fine mist which is very disagreeableto workmen in the vicinity and which rapidly corrodes all metal in theroom or building. The attack and solution of the metal is alsoundesirable because of the consequent loss of metal and of acid. whichcannot economically be recovered, and because of the fact that theprocess of solution is not uniform, but localized, causing pitting ofthe surface.

Heretofore the addition of so-called picklinginhibitors to the acid hasbeen proposed, such inhibitors possessing the property of retarding thesolution of iron in acid,

while not appreciably affecting the solution of its oxides. Among theinhibitors which have been proposed, sugars, proteins, and the salts ofcertain nitrogenous bases, such as quinoline ethiodide have foundconsiderable commercial use.

This invention consists in adding a small proportion of a member of anew class of extremely effective pickling inhibitors to an acid picklingbath. This class of inhibitors comprises alkylated thioureas, such asmay AND PICKLHVG METALS 5, 1928. Serial No. 824,066.

lkyl halides og polyhalides. For example, suBsfitfitEdthioureas sucli asdiphenylthiourea k rea,-plienikethylthicai a difig'p yltliioiirfea, etc.may be reactedwith ylahlafid ethyl b ql il b1 7 5 li .lfgpt 1 ,C -hlridc methylene dibromidgjthyl- ,liloride. A

dibron ide methylene d15r"oinide," etc. The halogen of the alky l halideapparently reacts with the sulphur atom of the thiourea with theformation of the hydrohalide of an amino-thioether, as follows:

In the above equations R and R may be aryl or alkyl groups, while R isan alkyl group and X a halogen. The substituted thiourea (1) probablyundergoes a molecular rearrangement to the imino or pseudo form (2),which reacts with the alkyl halide to form the alkylated thiourea (3),which may be considered a thioether. These compounds are also known asalkyl substituted pseudothioureas because they have the same empiricalformulae as the substituted thioureas, but have a different chemicalconstitution and hence also different properties.

If an alkylene dihalide be employed in place of the simple alkyl halidethe second alogen atom reacts further with the hydrogen on the nitrogenatom, producing an aliphatic heterocylic nucleus containing a sulphuratom between two carbon atoms, and which may therefore also beconsidered be obtained by the react on of'thioureas with as a thioethertype compound.

B: R R: BI n. ilk-I l nr-r z x-z'm Bx-N x-tn Brew-tn =s- -s-n+x- 11,---sm .nx- --s-- a, .231: Br-N Brr- @113513156 dibroihidfbutylene In thisequation again, R and R may be aryl or alkyl groups, while R is hydrogenor an alkyl group and X a halogen. The substituted thiourea (1) mayagain be considered as undergoing rearrangement to the form (2), whichreacts with the alkylene halide with the possible formation of anintermediate compound (3) and a final compound (4). Since theunsaturated five-membered cyclic nucleus containing non-adjacent sulphurand nitrogen atoms is termed a thiazole, the saturated compounds of thetype of (4) may be considered as derivatives of tetrahydrothiazole. Thisis, if diphenylthiourea is reacted with ethylene chloride, R and R arephenyl groups and R is hydrogen, and the compound (4) in equation IIabove is 2-phenyl-imino-3-phenyl-tetrahydrothiazole.

Similar cyclic arylated thioureas containing 4, 5, 6 or even more atomsin the saturated ring may be obtained by reacting a substituted thioureawith a dihalogenated aliphatic hydrocarbon with 1, 2, 3 or more carbonatoms between the halogen atoms.

The alkylated thioureas are, in general, basic in their reaction and arefairly soluble in acid solutions, readily forming salts such as thehydrochlorides, sulphates, etc. They probably owe their peculiarefiicacy to the presence of the basic nitrogen atom together; with asulphur atom in a thioether type molecule. However, it is to beunderstood that it is not intended to limit the scope of this inventionby any theories which have been or may be herein advanced, such theoriesbeing merely illustrative and explanatory in nature.

The particular substance or substances selected from this class ofpickling inhibitors should preferably be soluble in acid solutions,stable at normal or slightly elevated temperatures, and substantiallynon-volatile. These conditions are particularly well satisfied by thereaction products of the diaryl substituted thiroureas with ethylenechloride. The raw materials are inexpensive, the reaction is practicallyquantitative, and the products are crystalline. For example, to obtainthe 2- phenyl imino 3 phenyl tetrahydrothiazole mentioned above, 228parts by weight of diphenylthiourea, commonly known as thiocarbanilide,are mixed with 99 parts of ethylene dichloride and the mixture is heatedon a steam bath for 24 hours.

The reaction takes place according to the following equation, thehydrogen chloride probably adding on the nitrogen atoms to form thehydrochloride of the base:

um carbonate, and the insoluble base filtered OE and dried. The productis usually uite pure and is ready to use. The residue om the waterextraction, consisting chiefly of unreacted material, is added to thenext batch. The 2-phenylimino-3-phenyl-tetrohydrothiazole thus obtainedis only slightly soluble in water, but dissolves readily in acidsolutions, since its hydrochloride, sulphate, etc. are soluble.

EwampZe J.The following tests illustrate clearly the remarkableefiiciency of the products of this invention. Pickling solutions wereprepared containing respectively, 5% by weight of hydrochloric(muriatic) acid, 19% hydrochloric acid, 4% and 10% sulphuric acid. Eachof these was divided into several port-ions, one of which was used as acontrol. To the other portions were added various porportions of the2-phenylimino-3- phenyl-tetrahydrothiazole prepared as hereinabovedescribed, or of quinoline ethiodide, a substance which has heretoforebeen proposed as a very effective pickling inhibitor.

Test pieces of sheet steel, about 2 cm. x 5 cm. in size were cut from asingle sheet of metal. The metal strips were all given a preliminarytreatment in an acid solution to remove the scale, were washed, bent atright angles, and placed on edge, each in the bottom of a widemouthedbottle. Each bottle was completely filled with one of the acid solutionspreviously prepared, and closed with a rubber stopper pierced by a bentglass tube so arranged that tbe hydrogen gas evolved by the reaction ofthe acid with the metal displaced an equal volume of the liquid, whichflowed through the tube into a measuring device. The bottles were thenplaced in water baths maintained at constant temperatures, and thevolume of hydrogen evolved in a period of one hour was carefullymeasured. The results are tabulated below.

Volume of hydrogen evolved, in cubic centimeters Pickling solutionInhibitor 35,

5% H01 19% HCl 4% H2804 10%H1SO4 at60 C. at 40 C. at 60 C. at 60 G.

Control 0 56. 0 153. 0 l4. 5 62.0

quinoline 0.03% 21.2 2.6

ethiodide- Z-Phenylimino- 0. 03% 5. 4 1. 9 3 p h e n y l tetrahyd ro- 0.05% 9. 2 3 0 thlazole It is evident that the preferred products of thisinvention are extremely valuable in preventing the corrosion of iron andsteel in acid pickling baths after the scale has been dis- 252.COMPOSITIONS,

assumes solved, the negligible volume of hydrogen evolved indicatingthat the reaction of the acid with the iron is almost com letelychecked, and that they are far more e ective than even such previouslyproposed substances as quinoline ethiodide. However, the addition ofsuch inhibitors has practically no effect on the rate of solution of thescale or other oxide of the metal.

Similar tests of other reaction products of substituted thioureas withalkyl chlorides show that the members of this class in general areexcellent picklin inhibitors. The products prepared from itolylthioureaand ethylene dichloride, and from diphenylthiourea and ethyl chloride,for example, are practically as effective as the product obtained fromdiphenylthiourea and ethylene dichloride as hereinabove described.

Example 2.-A sample of 2 o-tolylimino 3 o-tolyl tetrahydrothiazole wasprepared by the reaction of ethylene dichloride with di-otolylthiourea,as described above, and the ethyl ether of diphenylthiourea wassimilarly prepared by reacting ethyl iodide with diphenylthiourea. Thesetwo products were compared with the 2 phenylimino 3 phenyltetrahydrothiazole in the following experiment.

Strips of sheet steel were prepared as described in Example 1 above andwere placed in flasks with 10% sulphuric acid without any inhibitor andwith the same solution containing 0.03% of the inhibiting materials.

The extent of the reaction of the acid with the iron was gauged in thiscase by weighing the metal strips before and after treatment in the 10%acid at C. for 20 minutes. The loss in weight of the iron in the controlsample was arbitrarily termed 100 and the losses in thenothersqll iionwere calculated in the same proportion;

In the practice of this invention on a commercial scale, an acidsolution containing hydrochloric or sulphuric acid is prepared in theusual manner and a small proportion of the inhibitor is dissolvedtherein, for example one pound of the inhibitor to from one hundred toone thousand pounds of acid being used. The metal, which is preferablyfirst degreased by treatment with an organic solvent or with an alkali,is treated in this bath in the customary manner, except that it may beleft in the solution for a longer time, since there is little danger ofoverpickling. Pittmg of the metal is almost completely eliminated, theconsumption of acid and of metal is very greatly reduced, andembrittlement of the metal and formation of acid mist due to theevolution of hydrogen gas is largely prevented.

Metals may be pickled or cleaned in the improved pickling solutionscontaining the inibitors of the class hereinabove described in manywidely different manner. For example, the metal may be completelyimmersed in the acid, if desired being carried into and out of thesolution by automatic devices which also wash and dry the metal; or thesolution may be sprayed onto the surface of the metal, and be laterwashed ofi' by a water spray. The concentration of the acid, and thetemperature of the solution may be varied as desired; and the inhibitorsmay be added in either greater or less proportions than described in theexamples above. It is evident that even proportions of less than 0.01%of the inhibitor are quite eifective, whereas comparatively largeproportions, up to several per cent. may be necessary to reduce thecorrosion of the metal to an absolute minimum. Although eitherhydrochloric or sulphuric acid is usually employed in pickling iron,because of the low cost of these substances, any of the othernon-oxidizing acids may be substituted therefor in whole or in part. Forexample, pickling solutions containing phosphoric or hydrofluoric acidare useful in many cases. Because of their remarkable stability, thealkylated thioureas may even be employed as inhibitors in picklingsolutions containing strong oxidizing acids such as nitric acid.

It will often be found convenient to add the requisite amount of theinhibitor to the concentrated acid at the time of manufacture or at anylater time, and simply dilute this s ock pickling acid containing theinhibitor to the desired concentration as it is needed. Such a stockpickling acid may for example be prepared by dissolving 1 part by weightof 2 phenylimino 3 phenyl tetrahydrothiazole in 500 parts ofconcentrated sulphuric acid.

While I have herein disclosed with considerable fparticularity certainpreferred manners o performing my invention, I do not thereby desire orintend to limit myself solely thereto, for, as hitherto stated, theprecise proportions of the materials utilized may be varied and othermaterials having equivalent chemical properties may be employed ifdesired without departing from the spirit and scope of the invention asdefined in the appended claims.

I claim:

1. The method of cleaning metals which comprises treating metals with asolution comprising a strong acid and a small proportion of an alkylsubstituted pseudothiourea.

2. The method of cleaning ferrous metals which comprises treatingferrous metals with a solution comprising a mineral acid and a smallproportion of an alkyl substituted aryl 5 pseudo-thiourea.

3. The method which comprises pickling iron or steel in a solutioncomprising a nonoxidizing mineral acid and a small proportion of asubstance selected from the class comprising alkyl substituted diarylpseudothiourea.

4. The method which comprises pickling iron or steel in a solutioncomprising a nonoxidizing mineral acid and a small proportion of asubstance selected from the class comprising cyclic alkylateddiaryl-thioureas.

5. The method which comprises pickling iron or steel in a solutioncomprising a nonoxidizing mineral acid and a small proportion of asubstance selected from the class comprising cyclic alkylateddiaryl-thioureas, the cycle containing 5 atoms.

6. The method which comprises pickling iron or steel in a solutioncomprising a non- 5 oxidizing mineral acid and a small proportion of 2phenylimino 3 phenyl tetrahydrothiazole.

7. A bath for cleaning or pickling metals comprising a strong acid and asmall proportion of an alkyl substituted pseudo-thiourea.

8. A bath for cleaning or pickling metals comprising a strong mineralacid and a small proportion of an alkyl substituted arylpseudo-thiourea.

9. A bath for cleaning or pickling metals, which comprises a strongmineral acid and a small proportion of a substance selected from theclass comprising alkyl substituted diaryl seudo-thiourea.

10. A bath for cleaning or pickling ferrous metals, which comprises astrong mineral acid and a small proportion of a substance selected fromthe class comprising cyclic alkylated diaryl thioureas.

11. A bath for cleaning or pickling iron or steel, which comprises anon-oxidizing mineral acid and a small proportion of a substanceselected from the class comprising cyclic alkylated diaryl-thioureas,the cycle containing 5 atoms.

12. A bath for cleaning or pickling iron or steel, which comprises anon-oxidizing mineral acid and a small proportion of a 2 arylimino 3aryl tetrahydrothiazole.

13. A bath for cleaning or pickling iron or steel, which comprises anon-oxidizing mineral acid and a small proportion of 2 phenylimino 3phenyl tetrahydrothiazole.

14. A bath for cleaning or pickling iron or steel, which comprisessulphuric acid and a small proportion of 2 phenyh'mino 3 phenyltetrahydrothiazole.

15. The method of cleaning metals which 55 comprises treating metalswith a solution comprisin a strong acid and a thioether containing aasic nitrogen atom.

16. The method which comprises pickling iron or steel in a solutioncomprising a nonoxidizing mineral acid and a small proportion of athioether containing a basic nitrogen atom.

17. A bath for cleaning or pickling iron or steel, which comprises astrong mineral acid and a small proportion of a thioether containing abasic nitrogen atom.

18. An aqueous solution of a non-oxidizing acid capable of dissolvingiron oxides to which has been added an inhibitor comprising an organicpseudo-substitution product of thiourea.

19. An aqueous solution of a non-oxidizing acid capable of dissolvingiron oxides to which has been added an inhibitor comprising an organicpseudo-substitution product of NH C(bHyNH in which the hydro en attachedto sulphur is replaced by an a yl group.

20. An aqueous solution of a non-oxidizing acid capable of dissolvingiron oxides to which has been added an inhibitor comprising a substancehaving the general formula Nit C(SR).NR in which R represents hydrogenor an alkyl or aryl group, and R represents an alkyl group.

21. The process of pickling iron and steel products which consists intreating said products with an aqueous solution of a nonoxidizing acidcapable of dissolving iron oxides to which has been added an inhibitorcomprising an organic pseudo-substitution product of thiourea.

22. The process of pickling iron and steel products which consists intreating said products with an aqueous solution of a nonoxidizing acidcapable of dissolving iron oxides to which has been added an inhibitorcomprising an organic seudo-substitution product of NH:C(SH). H in whichthe hydrogen attached to sulphur is replaced by an alkyl group.

23. The process of pickling iron and steel products which consists intreating said products with an aqueous solution of a non-- oxidizingacid capable of dissolving iron oxides to which has been added aninhibitor comprisin a substance having the general formula I51: C(SR).NRin which R represents hydrogen or an alkyl or aryl group, and Rrepresents an alkyl group.

In witness whereof I have hereunto set my hand this 4th day of December,1928.

WALDO L. SEMON.

